1. Field of the Invention
The invention concerns a coil arrangement for contact-less guidance of a magnetic object (in particular an endoscopy capsule) in a workspace.
2. Description of the Prior Art
The use of endoscopes and catheters has an ever increasing application in medicine for the diagnosis or treatment of the inside of a patient. The instruments are introduced into the body via bodily orifices or incisions and, directed from the outside, can be displaced in a longitudinal direction, for which a mechanical connection to the instrument is necessary. However, in the case of forward movement of the instrument in the body, difficulties in the navigation occur regularly at curves or branches, such that the operator must direct the instrument in the desired direction (possibly via repeated attempts) and a supporting force of the tissue on the instrument is required for the further navigation. This is associated with high time expenditure by the operator and pain for the patient. In the worst case it is not precluded that the guidance in the planned direction cannot be achieved at all, or that the risk of tissue perforation arises. Furthermore, in the case of endoscopy it can be of interest to rotate the endoscopy head (equipped with a camera) in specific directions, for example in order to be able to completely view the mucous membrane in a segment of the gastrointestinal tract. This is only conditionally possible with modern catheter endoscopes because the catheter tip has only limited mobility. Moreover, typical catheter endoscopes have the disadvantage that remotely situated internal organs can only be reached with difficulty, or cannot be reached at all.
The passive endoscopy capsule moved by the natural peristalsis of the gastrointestinal tract does not have the cited disadvantages of the catheter endoscope, but it cannot be navigated, meaning that the targeted viewing of specific points inside the gastrointestinal tract is not possible. Therefore, magnetic navigation or guidance systems have been proposed that enable a catheter-free wireless guidance of endoscopy capsules that embody a magnetic dipole moment. A catheter-free or wireless guidance is also designated as “contact-free” in the following.
DE 103 40 925 B3 and WO 2006/092421 A1 respectively describe a magnetic coil arrangement consisting of 14 individual coils for navigation of an endoscopy capsule, a video capsule or another probe. The capsule is hereby equipped with a magnetic element, for example a permanent or ferromagnet. The magnetic coil arrangement generates magnetic field components Bx, By, Bz along the axes x, y, z of a Cartesian coordinate system, as well as magnetic gradient fields that enable a contact-less guidance of the endoscopy capsule.
In such system, use is made of the fact that the magnetic element (i.e. a body with a magnetic dipole moment m) will attempt to align itself parallel to the direction of the magnetic field B consisting of the magnetic field components Bx, By, Bz in the direction of the axes of the Cartesian coordinate system. Since the magnetic element is firmly connected with the endoscopy capsule, the orientation of the capsule can thus be affected. A force F=G·m (initiated by the magnetic gradient fields ∂Bx/∂x etc.) additionally acts on the magnetic dipole moment m with a gradient matrix G comprising the gradient fields according to
  F  =            G      ·      m        =                  (                                                                              ∂                                      B                    x                                                  /                                  ∂                  x                                                                                                      ∂                                      B                    x                                                  /                                  ∂                  y                                                                                                      ∂                                      B                    x                                                  /                                  ∂                  z                                                                                                                          ∂                                      B                    y                                                  /                                  ∂                  x                                                                                                      ∂                                      B                    y                                                  /                                  ∂                  y                                                                                                      ∂                                      B                    y                                                  /                                  ∂                  z                                                                                                                          ∂                                      B                    z                                                  /                                  ∂                  x                                                                                                      ∂                                      B                    z                                                  /                                  ∂                  y                                                                                                      ∂                                      B                    z                                                  /                                  ∂                  z                                                                    )            ·      m      
Analogously to the magnetic field B, the force F and the magnetic moment m are thereby three-dimensional vectors with corresponding x-, y- and z-components. The 3×3 gradient matrix G is symmetrical and spur-free due to the Maxwell equations curl H=0 and div B=0, as well as due to B=μ0·H, meaning that—with ∂Bx/∂y (=∂By/∂x), ∂Bx/∂z (=∂Bz/∂x), ∂By/∂z (=∂Bz/∂y) and two of the three diagonal elements (for example ∂Bx/∂x and ∂By/∂y)—it contains five independent gradient fields.
The magnetic field B and the gradient fields can be adjusted arbitrarily via a targeted activation of the individual coils of the magnetic coil arrangement. It is therefore possible to rotate the magnetic object and thus to align it arbitrarily in a work space within the magnetic coil arrangement. Moreover, it is possible to exert a force F on the magnetic object in order to displace it translationally in addition to the rotation. For this eight quasi-static magnetic degrees of freedom are realized, namely the magnetic field components Bx, By, BZ as well as two of the three entries of the diagonal elements (for example ∂Bx/∂x and ∂By/∂y) and three of the secondary diagonal elements (for example ∂Bx/∂y, ∂Bz/∂x, ∂Bz/∂y) of the gradient matrix G.
The systems described in DE 103 40 925 B3 and WO 2006/092421 A1 have the disadvantage that they are relatively cost-intensive in their manufacture and installation due to the 14 individually activated coils that are required there due to the high number of coils and activation units (in the form of power amplifiers).